1. Field of the Invention
The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a device and method for transmitting data according to a radio link protocol (RLP) used for effective data transmission in radio environments.
2. Description of the Related Art
In general, CDMA mobile communication systems have developed from the IS-95 standard, which mainly provides voice service, into the CDMA-2000 standard, which provides high-speed data service as well as voice service. The CDMA-2000 standard can provide high-quality voice service, moving picture service and Internet search service.
FIG. 1 shows an exemplary packet data service defined by the CDMA-2000 standard. In FIG. 1, a mobile station (MS) includes a terminal equipment (TE) and a mobile termination (MT). A base station is represented by BS/MSC (Base Station/Mobile Switching Center), and an interworking function block (IWF) connects the BS/MSC to a data network (e.g., Internet). The IWF block is a device for converting between different protocols, when different protocols are used. In FIG. 1, the upper layer service (or Web service) processors of the mobile station and the IWF block form messages which are passed down through a network protocol (e.g., Internet protocol (IP)) processor and a link protocol (e.g., point-to-point protocol (PPP)) processor. Then, the data assembled by the upper layer service processors is finally transmitted to the lower layers in the form of a link protocol packet, and the lower layers transmit the data using a proper protocol (e.g., EIA-232, RLP, etc).
FIG. 1 shows an example where an EIA-232 controller is used between the TE and the MT. Generated RLP frames are transmitted over a physical channel connected according to the IS-2000 standard, which is part of the CDMA-2000 standard. The RLP packets received at the base station over the connected physical channel are restored back to link protocol packets and the restored packets are transmitted to the IWF block through the relay layer. In general, interfacing between the base station and the IWF block is performed according to the IS-658 standard. In the IWF block, the link protocol layer reads data from the link protocol packets and transmits the data to the network protocol processor, where the data is finally transmitted to the upper service processor. The distribution of link protocol packets into radio link protocol (RLP) frames through the RLP is one of the subjects of the present invention.
Above, a description has been made of a process for transmitting data from the mobile station to the base station, and it should be noted that the process for transmitting the data from the base station to the mobile station can be performed in a similar manner. To provide various services, the CDMA-2000 standard supports various schemes different from that of FIG. 1. However, the various schemes have a common feature in that the link protocol packets with the upper service data are transmitted over the physical radio channel through the RLP.
The RLP Type-3 specification generates only the RLP frame having a proper size to fill either a physical channel frame of 9.6 Kbsp or 19.2 Kbps for the current Rate Set 1, or the RLP frame having a proper size to fill either a physical channel frame of 14.4 Kbps or 28.8 Kbps for the Rate Set 2. Therefore, when the physical channel operates at the higher rate of 153.6 Kbps or 230.4 Kbsp, a method is used for filling several RLP frames in one physical channel frame. If the physical channel supports a rate over 153.6 or 230.4 Kbps (which is the maximum rate supported in the RLP Type-3 specification), for example, if the physical channel supports the rates of 307.2 Kbps, 460.8 Kbps, 614.4 Kbps and 1036.8 Kbps, more RLP frames can be filled in one physical channel frame. However, as compared with the method for filling one physical channel with one large-sized RLP frame, this method causes an increasing burden on the frame header and creates unusable parts of the frame, thereby decreasing the frame efficiency. Therefore, to transmit a RLP frame with a size larger than the current RLP Type-3 frame, a new method is required.
An important operation performed by the RLP Type-3 is to create and analyze a segmented frame. That is, when a size of the retransmission frame to be transmitted is larger than a size of the data block which can be transmitted, the RLP segments a data portion (or portion) of the retransmission frame to be transmitted into several segmented frames. The RLP Type-3 specification performs the segmentation procedure as follows.
First, the RLP Type-3 can create a maximum of 3 segments. The respective segments are distinguishable with three values of FIRST, SECOND and LAST. When more than 3 segments are required, the RLP Type-3 does not transmit the retransmission frame until it is possible to transmit the retransmission frame with three segmented frames.
Second, a reassembly procedure for the segmented frames is performed only after all of the segments are received. That is, if any one of the FIRST, SECOND and LAST segmented frames is not received, it is necessary to retransmit all the segments.
The RLP Type-3 specification creates an RLP frame of a size which is filled in the physical channel frame of 9.6 Kbps or 19.2 Kbps at the Rate Set 1, and an RLP frame of a size which is filled in the physical channel frame of 14.4 Kbps or 28.8 Kbps at the Rate Set 2, so that it is possible to transmit a maximum of 3 segments even at the 9.6 Kbps or 14.4 Kbps, which is the lowest transmission rate. However, when the physical channel uses the larger RLP frame to increase transmission efficiency at the higher transmission rate, a new segmentation method is required which is different from the existing segmentation method.